Organic Light Emitting Diode (OLED) has been widely used in the field of display, lighting and smart wearable for its advantages of good self-luminous characteristics, high contrast, fast response and flexible display and etc.
With the development of science technology, OLED technology has become an important candidate for the third generation of display technology used for consumer electronics such as mobile phones, computers, televisions, etc. The basic display principle of OLED is as follows: driven by an electric field, the organic material emits light by the injection and recombination of carriers. OLED can be independently illuminated by RGB pixels, white OLED combined with color filter or blue OLED with light color conversion to achieve full color display. OLED display technology can make the panel thinner; its self-luminous characteristics can also achieve higher contrast in the wild evening, and can be made on the substrate of different materials, and can be made as a flexible display device.
Green environment and energy-efficient way of life has become the trend of people's lives, so OLED is considered as the future lighting technology. Light-emitting materials of OLED are organic semiconductors; the material properties of the light-emitting layer can be controlled to produce light with different wavelengths. OLED is a planar light source with soft light. Its illumination can achieve thinner, if the OLED is fabricated on a flexible substrate, it can realize a large area and a flexible light source, and has potential applications in home decoration and the like.
Smart wear market will be an important direction for OLED technology development. The thin, flexible and portable properties of flexible AMOLEDs (active matrix organic light-emitting diodes) determine that there will be wider room for application on wearable devices. OLED display panel can be equipped to a bracelet or watch; it can achieve the perfect fit with the wrist, but also can realize making calls, internet and other functions.
In addition, OLED has potential applications in car audio display, smart home, aerospace technology.
The difference between OLED and conventional LCD is that a backlight is no more needed, through the carriers of both electron and hole to inject the organic thin-film organic materials and recombination to emit light in the organic materials. However, the organic materials are very sensitive to moisture and oxygen. The permeation of water/oxygen is greatly reducing the lifetime of the device. To meet the commercialized requirements for the lifetime and stability of OLED device, the OLED devices have very high requirements for encapsulation: the lifetime is at least 104 hours, the transmission rate of water vapor is less than 10−6 g/m2/day, and the transmission rate of oxygen is less than 10−5 g/m2/day (1 atm). Therefore, encapsulation in the fabrication of OLED devices is in an important position, is one of the key factors affecting the yield of the product.
The encapsulation methods for existing OLED device mainly include glass encapsulation, that is, the encapsulation glass is coated with a UV light curable sealant, a laser sealing for laser-encapsulation, or a sealant and filing a Dam & Fill desiccant and cured to provide a relatively confined environment for the light-emitting device, to achieve good water/oxygen barrier capability in a certain period of time.
Flexible OLED panel is an important research direction of organic light-emitting devices. In recent two years, the exploration of encapsulation of flexible OLED devices is in full swing. Thin film encapsulation using plasma enhanced chemical vapor deposition, PECVD or atomic layer deposition, ALD has become a research hotspot. However, the encapsulation cost of flexible OLED devices is 1 to 5 times of the cost of conventional cover encapsulation devices. Although the flexible OLED display is the future trends, but the conventional flat glass OLED encapsulation device does not disappear.
TFTs play an important role in active matrix driven display devices, AMOLEDs, typically as switching devices and driving devices in display devices. By the high UV light energy, TFTs generate carriers, electrons or holes under light irradiation, when the free carrier concentration increases, the threshold voltage, Vth decreases, and the Vth shifting directly causes the luminance of the pixel to be changed, thereby affecting the overall display quality. Therefore, the long-term stability of the TFT display device is very important.
The encapsulation for large-size devices need to add filler to improve the mechanical properties of the device, in addition to eliminate Newton ring (especially for top-emitting devices, Newton rings must be eliminated). Currently filler has two major categories according to the method for curing: UV light curing and thermal curing. Wherein, UV light curing process is simple, curing time is short, usually 5 min-15 min, Tact time of mass production can be shortened; its shortcomings are UV light is irradiated to the device from a side of the cover plate, during trigger curing of the filler, it causes TFT electrical shift at the same time, reducing the overall image display quality. A temperature of thermal curing of the Filler currently in the market is about 100° C., curing time up to 60 min-90 min; In addition, the temperature uniformity of the oven adapted has a significant impact on the degree of curing the filler, uneven curing of the filler will result encapsulation mura (phenomenon of uneven brightness of the display device).
FIG. 1 is a schematic diagram of a conventional encapsulation process of OLED, as shown in FIG. 1, an existing encapsulation structure of OLED includes a TFT substrate 100 and an encapsulation cover plate 200 disposed opposite to each other, an OLED device 300 disposed between the TFT substrate 100 and the encapsulation cover plate 200 and disposed on the TFT substrate 100, a sealant 600 disposed between the TFT substrate 100 and the encapsulation cover plate 200 and forming a sealed space 610 between the TFT substrate 100 and the encapsulation cover plate 200, an encapsulation material 700 filled in the sealed space 610.
As shown in FIG. 1, when the encapsulation material 700 is UV light cured from a side of the encapsulation cover plate 200, when the encapsulation material 700 is solidified by the UV light, at the same time, the performance of the TFT device in the TFT substrate 100 is affected, and cause the TFT device in the TFT substrate 100 to electrically shifted, and reduce the overall image display quality.